The present invention relates to a vertical mill gearbox.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
Vertical mill gearboxes are known in various designs and are used to convert torque and speed in magnitude and direction, and to accommodate and support process loads. A vertical mill gearbox can have a first planetary stage to drive a second output-end planetary stage. During grinding process, vibrations are generated which excite natural frequencies of the drive train formed, i.a., by a motor, a coupling, and a drive shaft that is driven by the motor and coupling. Such natural frequencies can destroy the drive train at least in parts or completely. Usually the weakest element in the drive train is the most prone to damage. In vertical mill gearboxes this is usually a bevel-gear stage formed by a bevel-gear pinion and a bevel gear. The purpose of the bevel-gear stage is to convert the torque and speed in respect of magnitude and direction. The torque is transmitted from the bevel gear pinion to the bevel gear. The latter transfers the torque to a vertical intermediate shaft. Resulting forces in the toothing cause the intermediate shaft to be deformed, thereby affecting the load-bearing behavior of the planetary pre-stage. For statically determinate design, planetary stages require at least one freely adjustable member which in a vertical mill gearbox is constituted by a planet carrier. As a result of the equilibrium of forces arising and manufacturing tolerances achieved, the toothed gears rolling off into one another can freely adjust and can shift the planet carrier radially with respect to a rotation axis within a small and permissible range. In addition, these displacements of the planetary pre-stage have an effect on the load-bearing behavior of the bevel-gear stage. Studies have also shown that deformations due to the forces of the bevel-gear stage are superimposed on process-load-induced deformations and displacements of other elements of the vertical mill gearbox.
Process loads resulting from the grinding operation, the displacements of the adjustable-movement members of the planetary stages and the deformation resulting from the bevel-gear stage adversely affect the load-bearing behavior of the toothing in the planetary pre-stage and the bevel-gear stage. In addition, the bevel-gear stage is prone to vibrations and jolts caused by the process loads. Additional stress therefore builds up in the drive train, causing damage or requiring overdimensioning.
It would therefore be desirable and advantageous to provide an improved vertical mill gearbox to obviate prior art shortcomings.